1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus and specifically, to a flexible substrate structure for transmission and reception of signals, used in a rotating head unit for broadband storage such as a video tape recorder (VTR) and the like.
2. Description of the Related Art
In a magnetic recording and reproducing apparatus such as VTR and the like, a rotating head unit for carrying out recording and reproducing of external information is provided. In this rotating head unit, a flexible substrate is generally used as a support for signal lines for transmission and reception of signals from and to a rotary transformer, and on the flexible substrate, a plurality of signal lines and grand lines are provided.
In general, in order to prevent influence of external electromagnetic interference noises, a shield layer is formed on the flexible substrate, opposed to the plurality of signal lines. However, because the shield layer causes an increase of capacitance, the shield layer is formed not as a whole surface shield layer but, for example, as a mesh type of shield layer etched in a grid shape. The mesh type of shield layer is formed on the plurality of signal lines at equal intervals i.e., areas of the coated portions and the uncoated portions in the shield layer are almost equal.
However, in the flexible substrate structure for transmission and reception of signals in the conventional magnetic recording and reproducing apparatus described above, there is a problem that the transmission characteristic is deteriorated. A loss in transmission of signals naturally occurs due to the capacitance between the signal lines or between the signal line and the shield layer, when the structure is used in the rotating head unit for a broadband storage. Also, there is a problem that if the loss in transmission is compensated for by addition of other parts, manufacturing cost can be increased.
Therefore, the present invention is made in order to solve the above problems. Thus an object of the present invention is to provide a structure for a magnetic recording and reproducing apparatus including a flexible substrate for transmission and reception of signals, that is capable of preventing deterioration of the transmission characteristic without increasing cost, by suppressing the capacitance between signal lines and a shield layer.
In order to solve the above problems, according to a first aspect of the present invention, there is provided a magnetic recording and reproducing apparatus comprising: a flexible substrate on which is formed a plurality of signal lines for transmission and reception of signals from and to external circuits and grand lines; and a shield layer formed to be opposed to the signal lines and the grand lines, wherein portions of the shield layer covering each member of a pair of signal lines among the plurality of signal lines are different in area from one another.
Also, according to a second aspect of the present invention, there is provided a magnetic recording and reproducing apparatus wherein each pair of the plurality of signal lines comprises balanced signal lines that are connected to the terminals of a differential amplifier. In this aspect of the present invention the area of the shield layer covering the signal lines connected to an inverting input terminal of the differential amplifier is smaller than area of the shield layer covering the signal lines connected to a non-inverting input terminal.
Also, according to a third aspect of the present invention, there is provided a magnetic recording and reproducing apparatus wherein a plurality of openings is formed in the shield layer oppositely facing and covering the signal lines. The areas of the portion of the shield layer covering the signal lines are different according to the number of the openings provided in the shield layer.
Also, according to a fourth aspect of the present invention, there is provided a magnetic recording and reproducing apparatus wherein a plurality of openings is formed in the shield layer oppositely facing and covering the signal lines. The areas of the portion of the shield layer covering the signal lines are different according to the size of the openings provided in the shield layer.
Also, according to a fifth aspect of the present invention, there is provided a magnetic recording and reproducing apparatus wherein signals transmitted to the signal lines are broadband signals.